This invention relates generally to robot mechanisms for moving workpieces from one processing location to another and, more particularly, to techniques for automatically calibrating a robot mechanism after assembly or maintenance. Robot mechanisms of various designs have been employed to facilitate the movement of substrates in the fabrication of semiconductor devices. Such mechanisms can be programmed to move planar substrates between processing locations, which are usually in a vacuum or clean environment. Robot mechanisms of this general type have in common the need to be properly calibrated upon installation or after maintenance or disassembly.
Some robot control systems have a programming mode in which a mechanism is "taught" its required steps under manual control, and will then be able to perform the same steps automatically. In most manufacturing applications of robots, the sequence of steps that a robot mechanism is required to perform will be well defined. There is not usually a need for frequent reprogramming of the sequence, but there is a need for calibration of the system to account for changes in the robot mechanism's position with respect to the environment in which it operates, or for differences between actual and theoretical positions of objects in the robot's environment.
More specifically, a robot mechanism may be installed in a vacuum chamber that is surrounded by various processing chambers. The purpose of the present invention is to compensate for any differences between the actual and predicted positions of the robot mechanism with respect to the vacuum chamber and with respect to the processing chambers.